This dissertation details efforts to image the properties of the Alaska-Aleutian subduction zone using several dense seismic deployments (164oW–138oW) and various seismic techniques, earthquake detection and locations, P-to-S mode conversions from local earthquakes, and receiver functions (RFs). Chapter 2 investigates if subduction is the source of the Wrangell volcanic field volcanism (WVF) using detection and location algorithms on a dense seismometer array (15 km spacing) to increase and refine the earthquake catalog. This reveals a dipping layer of seismicity, oblique to plate motion, extending 100 km below the WVF and a tear between the WVF and the adjacent, well-imaged subduction zone. The tear and oblique subduction contribute to high volcanism and low seismicity below the WVF. Chapter 3 develops a new method to image the subduction zone below the Kenai Peninsula using previously underutilized arrivals from local in-slab earthquakes converting from P-to-S at the plate interface (PS). The amplitude of the PS arrival compared to P (APS_P) maps out changes in plate interface properties with depth, low APS_P in shallow locked regions, and high APS_P deeper. From 1D modeling, the high APS_P requires a complex, layered region representing a thick shear zone of varying lithologies or high pore fluid pressures at the plate interface. This heterogeneous plate interface model contrasts the homogenous low-velocity layers (LVLs) typically observed in RF images. Chapter 4 investigates this discrepancy using local and teleseismic P-to-S conversions recorded across the Kodiak, Semidi, and Shumagin segments. Ray tracing and 2D full waveform modeling through self-consistent velocity models show local PS arrivals convert 1-10 km shallower than the RF dominant peak, associated with the subducting plate Moho, and elongated scatterers are required in the upper region of the subducting plate. Due to the lower frequency content, RFs are insensitive to sub-km scale heterogeneity required by local PS. What constitutes the LVL likely changes with depth, from hydrous minerals, fluids, or sediments (<40 km deep) to oceanic crust deeper. The scatterers also change from a mélange of metasediment, metabasalt, lenses of pore fluid, or hydrous minerals to metamorphosed, heavily sheared oceanic crust and fluid migration deeper.